The present invention relates to a process for controlled evolution of wine by electrochemical way and to the relevant electrochemical reactor.
The evolution of wines is a series of processes taking place after the phases of alcoholic fermentation of must and subsequent malolactic fermentation; such processes can be generally subdivided into a maturation step, consisting of a series of oxidative processes in the presence of small quantities of oxygen, and an optional aging step, in the absence of oxygen. The evolution of a wine starting from the termination of the fermentation steps up to the commercialisation normally requires pretty long times especially for high quality wines, involving rather high costs. The maturation step, in particular, is extremely critical as known to those skilled in the art, since excessive amounts of oxygen would cause the undesirable process of acetic fermentation, with irreparable deterioration of the product; in order to supply a controlled amount of oxygen, the maturation is traditionally carried out with wooden casks, known in the art as barriques, favouring the micro-oxygenation of wine through natural permeation across the porosity of their walls. The high price of the barriques and the lengthy treatment times nevertheless negatively affect the product cost. A commonly practised alternative consists of maturing wine in metal tubs, in which a controlled amount of air is bubbled; also this solution is however expensive, not very efficient (especially due to the insufficient homogeneity in the distribution of air within the bulk of treated wine) and generally unsuitable to sensibly reduce the treatment times.
More recently, wine micro-oxygenation processes by electrochemical way have been proposed, for instance according to the disclosure of US 2004/0137109: the controlled evolution of small amounts of oxygen on the surface of high surface area titanium anodes immersed in the wine to be treated, at current densities typically comprised between 1 and 500 μA/cm2, favours the accelerated evolution thereof.
However the improved process of US 2004/0137109 still has some inconveniences: the passage of anodic micro-currents through titanium anodes in fact takes place at very high potentials, largely above 1 V (vs. Ag/AgCl), whereat oxygen evolution is an inevitable process. Although such process allows remarkable savings on the treatment time for maturation, it has for instance no effect on the characteristics deriving from the aging of wine, that is on the process phase traditionally occurring after the bottling, rigorously in the absence of oxygen, which requires prolonged times with the associated capital and storage costs.
Furthermore, the result obtained in terms of organoleptic properties, although not negligible, is still distant from what obtainable with the traditional manufacturing, for instance by maturation in barrique, because the chemistry associated with these processes is very complex and involves reactions preferentially taking place at potentials below the one of oxygen discharge on titanium; this applies in particular to the polymerisation and stabilisation reactions of some compounds with colouring properties. The wine obtained immediately after the fermentation steps is rich in phenolic compounds, the most important of which belong to the families of flavonoids and anthocyans. The latter in particular, together with the anthocyanidins which are a common derivative thereof, are responsible of the purple colour of new wines and tend to undergo structural transformations during the maturation and aging steps, for example by association with other phenolic compounds such as flavanols giving colourless compounds, or aggregating in polymers which tend to precipitate due to their poor solubility, bestowing wine with progressively lighter colours tending to orange or brick. As it can be experimentally noticed both by chromatographic analysis and by organoleptic determination, the equilibrium of these complex reactions is not exactly respected by the known electrochemical treatments carried out with micro-currents at oxygen discharge potential.